Hidden Chemistry at Solar Biggie BrightSource

We don’t have too many rules here in C&EN blogville, but we do try to maintain a chemistry connection. I was worried that would be at risk if I were to post about BrightSource Energy, a mega solar tech firm that has filed for a $250 million IPO.

BrightSource Energy's solar mirrors. Credit: BrightSource

To generate energy from the sun, BrightSource puts thousands of big mirrors in the desert that track the sun and focus light on a tower with a boiler full of water. The steam generated cranks a turbine to create electricity. It sounds like what a technology firm would think up if someone forgot to invite a chemist or chemical engineer to the concept meeting. [Note that in contrast, other solar thermal companies use nifty heat-transfer fluids like biphenyl and diphenyl oxide, as described by my colleague Alex Tullo.]

But there are at least two innovative uses of chemistry in the BrightSource system, one is basic CRC handbook stuff and one is rather mysterious. To extend the hours during which the water can be turned into steam, BrightSource is working to store some of the sun’s heat in a blend of molten nitrate salts (sodium nitrate and potassium nitrate). To save you the Googling, the melting point of sodium nitrate is 308 C and potassium nitrate is 334 C. For some reason this nice detail is in the firm’s S1 filing but I did not see it on the website.

The more mysterious chemistry is alluded to on the company’s website. As you can imagine, the boiler tower has to withstand some unusual conditions. But worry not, because, “The boiler is designed to withstand the rigors of the daily cycling required in a solar power plant over the course of its lifetime, and is treated with a proprietary solar-absorptive coating to ensure that maximum solar energy is absorbed in the steam. [emphasis mine]. Hmmmmm…. I wonder what is in that coating? Tell me what you think.

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